Modified ball bond shear test for determination of adhesion strength of cold spray splats

Abstract

A modified ball bond shear test was developed to measure the adhesion of cold sprayed splats to both bulk substrates and cold sprayed coatings. The technique was applied to the deposition of Ti feedstock powder (spherical morphology, 29 m average dia.) onto a commercially pure bulk Ti plate and onto Ti coatings prepared with the same feedstock powder as the splats. Both an adhesion strength and adhesion energy were measured, with trends in adhesion examined as a function of in-air particle velocities between 580 and 825 m/s.Comparisons between cold spray splat on bulk materials versus coatings were conducted for two deposition conditions (694 and 825 m/s). Generally, the adhesion for splats deposited at the higher deposition condition were insensitive to the substrate material, while splats deposited at the lower deposition condition adhered better to the bulk material than to the coatings.3

Mechanical behavior of Ti cold spray coatings determined by a multi-scale indentation method

“…Along with this indication of increased bonding, the splats became more deformed and pan-caked. While these observations are for Ti onto Ti, similar observations have been made for Ti deposited on mild steel [28].…”

“…Single splats were deposited by increasing the gun traverse speed to 1 m/s and by decreasing the powder feeding rate to 1-5 g/min in the same manner as previously reported [28]. The splats deposited with nitrogen gas were produced at a different time frame than coatings and the in-flight particle velocity was re-measured prior to sample preparation.…”

“…The splat adhesion strength of cold sprayed Ti splats was tested using a Micro-Combi Scratch Tester (CSM Instruments, Inc., Needham, MA). A previously published splat adhesion strength testing procedure was used [28].…”

“…The gas temperature has been previously shown to have an effect on particle adhesion and can affect the hardness loss parameter [28]. Separate study is required to define the intercept velocity for coatings deposited with He.…”

“…Many complex phenomena take place during deposition, including: work hardening, formation of adiabatic shear instabilities and recrystallization [21][22][23][24]. The plastic deformation and formation of the adiabatic shear instability are believed to contribute to the bonding [25][26][27][28] for both particle to substrate (i.e. coating adhesion) and particle to particle (i.e.…”